[FAQ] Can I connect two outputs from a logic device together directly?

The primary concern with connecting outputs together is called "bus contention."

If one output is driving HIGH and the other output is driving LOW, then you have bus contention, and the device can be damaged. Here's an example with a fairly typical LVTTL driver:

In the above image, one CMOS output is represented as a single pair of nMOS and pMOS transistors. This is a very typical arrangement for CMOS outputs.

If we use a 5V supply for Vcc, it is easy to calculate the expected current as Iout = 5/(25+25) = 100mA. The current exceeds the datasheet absolute maximum for most logic CMOS outputs, and would likely damage the device.

It is possible to parallel channels of a device to increase drive strength -- it is just important to ensure that both outputs are always in the same state. The best way to achieve this is to use two channels in the same device, and to directly connect the inputs together to ensure they will always have the same state.

Looking for a low voltage translator? Check out the AXC family that supports 0.7V to 3.3V translation!

The Logic Minute training page has videos on many interesting topics that all are kept shorter than 5 minutes.